Phosphor and light-emitting device

ABSTRACT

A high-brightness phosphor having high-temperature characteristics and long-term reliability, and a white light-emitting device using this phosphor are provided. The phosphor contains a silicate phosphor (A) having a peak wavelength of at least 525 nm but not higher than 535 nm and fluorescence intensity of at least 250% but not higher than 270%; an oxynitride phosphor (B) having a peak wavelength of at least 540 nm but not higher than 545 nm and fluorescence intensity of at least 260% but not higher than 280%; and an oxynitride phosphor (C) having a peak wavelength of at least 645 nm but not higher than 655 nm, wherein the amount of the silicate phosphor (A) is at least 20% but not higher than 35% by mass, the amount of the oxynitride phosphor (B) is at least 50% but not higher than 70% by mass, and the amount of the oxynitride phosphor (C) is at least 10% but not higher than 20% by mass.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of International Application No.PCT/JP2012/070390, filed Aug. 9, 2012, which claims the benefit ofJapanese Application No. 2012-026586, filed Feb. 9, 2012, in theJapanese Patent Office. All disclosures of the document(s) named aboveare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a phosphor used for a light emittingdiode (LED) and a light-emitting device using an LED.

2. Description of the Related Art

As a phosphor used for a white light-emitting device, a combination ofβ-SiAlON and a red light-emitting phosphor is known (Patent Literature1). A phosphor combining a red light-emitting phosphor and a greenlight-emitting phosphor that has specific color coordinates is disclosedby (Patent Literature 2).

CITATION LIST Patent Literature

Patent Literature 1: JP 2007-180483 A

Patent Literature 2: JP 2008-166825 A

SUMMARY OF THE INVENTION Technical Problem

A purpose of the present invention is to provide a phosphor achievinghigh brightness and high color-rendering properties at the same time byadding an oxynitride phosphor to an existing phosphor. Another purposeis to provide a white light-emitting device using this phosphor.

Solution to Problem

The phosphor of the present invention includes: a silicate phosphor (A)having a peak wavelength of at least 525 nm but not higher than 535 nmand fluorescence intensity of at least 250% but not higher than 270%; anoxynitride phosphor (B) having a peak wavelength of at least 540 nm butnot higher than 545 nm and fluorescence intensity of at least 260% butnot higher than 280%; and an oxynitride phosphor (C) having a peakwavelength of at least 645 nm but not higher than 655 nm, wherein theamount of the silicate phosphor (A) is at least 20% but not higher than35% by mass, the amount of the oxynitride phosphor (B) is at least 50%but not higher than 70% by mass, and the amount of the oxynitridephosphor (C) is at least 10% but not higher than 20% by mass.

Assuming the amounts of the silicate phosphor (A) and that of theoxynitride phosphor (B) are a and b, respectively, it is preferable thatthey have the following relation: 1.5≦b/a≦3.5.

Assuming the amounts of the silicate phosphor (A), that of theoxynitride phosphor (B), and that of the oxynitride phosphor (C) are a,b, and c, it is preferable that they have the following relation:4.0≦(a+b)/c≦8.2.

It is preferable that the oxynitride phosphor (B) is β-SiAlON, and theoxynitride phosphor (C) is CASN.

The invention from another viewpoint as claimed herein is alight-emitting device having the above-described phosphor and an LEDthat mounts the phosphor on its light-emitting surface.

Advantageous Effects of Invention

According to the present invention, a high-brightness phosphor havinghigh-temperature characteristics and ensuring long-term reliability, anda white light-emitting device using this phosphor can be provided.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

The phosphor of the present invention includes: a silicate phosphor (A)having a peak wavelength of at least 525 nm but not higher than 535 nmand fluorescence intensity of at least 250% but not higher than 270%; anoxynitride phosphor (B) having a peak wavelength of at least 540 nm butnot higher than 545 nm and fluorescence intensity of at least 260% butnot higher than 280%; and an oxynitride phosphor (C) having a peakwavelength of at least 645 nm but not higher than 655 nm.

By mixing these phosphors (A), (B), and (C), a high-brightness phosphorhaving high-temperature characteristics and ensuring long-termreliability is obtained.

The amount of the silicate phosphor (A) is at least 20% but not higherthan 35% by mass, the amount of the oxynitride phosphor (B) is at least50% but not higher than 70% by mass, and the amount of the oxynitridephosphor (C) is at least 10% but not higher than 20% by mass.

If the amount of the silicate phosphor (A) is too low, thecolor-rendering properties tend to degrade, whereas if it is too high,high-temperature characteristics and long-term reliability tend not tobe ensured easily, which is why the above range is preferable.

If the amount of the oxynitride phosphor (B) is too low,high-temperature characteristics and long-term reliability tend not tobe ensured easily, whereas if it is too high, high color-renderingproperties tend not to be obtained. Similarly, if the amount of theoxynitride phosphor (C) is too low, high color-rendering properties tendnot to be exhibited, and in extreme cases, white light itself tends notbe obtained. If the amount is too high, the brightness tends todecrease, and in extreme cases, white light tends not be obtained.

The phosphor (A) of the present invention is a green light-emittingsilicate phosphor having a peak wavelength of at least 525 nm but nothigher than 535 nm and fluorescence intensity of at least 250% but nothigher than 270%. Specifically, G3161, EG2762, EG3261, and EG3560 byIntematix, and SGA-530 and SGA-535 by Merck are available.

The fluorescence intensity of the phosphor is expressed in a percentagevalue relative to the peak height of standard sample (YAG, morespecifically P46Y3 by Mitsubishi Chemical Corporation), which isregarded as 100%. To measure the fluorescence intensity, F-7000spectrophotometer by Hitachi High-Technologies Corporation was used. Themeasurement method is described below.

Measurement Method

1) Setting samples: A measurement sample or a standard sample was packedin a quartz cell, and measurement was performed by setting the samplesto a measuring apparatus alternately. The samples were packed in thecell up to approximately ¾ of the height of the cell, with the relativepacking density maintained at approximately 35%.

2) Measurement: The samples were excited using a light of 455 nm, andthe maximum peak height in a range from 500 nm to 700 nm was read.Measurement was performed five times, and the remaining three valuesexcluding the maximum and the minimum values were averaged.

The phosphor (B) of the present invention is a green light-emittingoxynitride phosphor having a peak wavelength of at least 540 nm but nothigher than 545 nm and fluorescence intensity of at least 260% but nothigher than 280%. Specifically, β-SiAlON, and more specificallyALONBRIGHT (registered trademark) by DENKI KAGAKU KOGYO KABUSHIKI KAISHAis available.

The phosphor (C) of the present invention is an oxynitride phosphorhaving a peak wavelength of at least 645 nm but not higher than 655 nm.Specifically, it is a phosphor abbreviated as and called CASN. Morespecifically, BR-101A (peak wavelength: 650 nm) by Mitsubishi ChemicalCorporation, R6634 (peak wavelength: 650 nm) and R6733 (peak wavelength:655 nm) both by Intematix are available. To this oxynitride phosphor(C), R6436 (peak wavelength: 630 nm) or R6535 (peak wavelength: 640 nm)by Intematix, or BR-102C, BR-102F (peak wavelength: 630 nm) or BR-102D(peak wavelength: 620 nm) by Mitsubishi Chemical Corporation may beadded for adjustment in an amount smaller than that of the oxynitridephosphor (C).

It is preferable that the amount of the silicate phosphor (A) is lowerthan that of the oxynitride phosphor (B) in order to maintain highreliability, and assuming the amounts of each are a and b, respectivelyit is preferable that the following relation is maintained: 1.5≦b/a≦3.5.

It is preferable that the amount of the oxynitride phosphor (C) is lowbecause the brightness of the oxynitride phosphor (C) itself is low.However, if the amount is too low, the color-rendering properties alsodecrease. It is therefore preferable that the ratio falls within thefollowing range: 4.0≦(a+b)/c≦8.2.

The method for mixing the silicate phosphor (A), oxynitride phosphors(B) and (C) can be selected as required, provided that they can be mixeduniformly or to a desired mixed state. A precondition of this mixingmethod is that entry of impurities is not allowed and that the shape andthe particle size of the phosphors do not change.

The invention from another viewpoint as claimed in the applicationconcerned is, as described previously, a light-emitting device havingthe above-described mixed phosphors and an LED that mounts the phosphorson its light-emitting surface. The phosphors mounted to thelight-emitting surface of the LED are sealed by a sealing agent. Resinand glass are available as the sealing agent, and the resin includessilicone resins. As the LED, it is preferable that a red light-emittingLED, blue light-emitting LED, and LED emitting other colors are selectedas required depending on the light to be emitted ultimately. In the caseof the blue light-emitting LED, the one made of a gallium nitridesemiconductor, and having a peak wavelength of at least 440 nm but nothigher than 460 nm is preferable. More preferably, the peak wavelengthis at least 445 nm but not higher than 455 nm. The size of thelight-emitting part of the LED is preferably 0.5 mm square or larger,and LED chips of any size can be selected, provided that they have thelight-emitting part area as described above. The area preferably is 1.0mm×0.5 mm, and more preferably 1.2 mm×0.6 mm.

EXAMPLE

Examples of the present invention will be described in detail byreferring to Tables and Comparative Examples.

TABLE 1 Peak Fluorescence wavelength intensity phosphor (nm) (%)Manufacturer, Model No. Phosphor(A) P1 512 242 EG2060 by Intematix P2525 253 EG2762 by Intematix P3 530 264 SGA530 by Merck P4 540 251 EG3759by Intematix phosphor(B) P5 538 218 ALONBRIGHT F4-SW by DENKI KAGAKUKOGYO KABUSHIKI KAISHA P6 542 269 ALONBRIGHT GR-MW540H by DENKI KAGAKUKOGYO KABUSHIKI KAISHA P7 552 220 ALONBRIGHT GR-LW555B by DENKI KAGAKUKOGYO KABUSHIKI KAISHA phosphor(C) P8 650 161 CASN BR-101A by MitsubishiChemical Corporation P9 630 166 S-CASN BR-102C by Mitsubishi ChemicalCorporation

The phosphors shown in Table 1 are the silicate phosphor (A), oxynitridephosphors (B) and (C) of the present invention. Of the silicate phosphor(A) in Table 1, P2 and P3 are phosphors satisfying the conditions thatthe peak wavelength is at least 525 nm but not higher than 535 nm andthat the fluorescence intensity is at least 250% but not higher than270%. Of the oxynitride phosphor (B) in Table 1, P6 only is a phosphorthat satisfies the conditions that the peak wavelength is at least 540nm but not higher than 545 nm and that the fluorescence intensity is atleast 260% but not higher than 280%. Of the oxynitride phosphor (C) inTable 1, P8 only is a phosphor that satisfies the condition that thepeak wavelength is at least 645 nm but not higher than 655 nm.

By mixing these phosphors at the ratio shown in Table 2, the phosphorsaccording to the Examples and Comparative Examples were obtained.

TABLE 2 Example Comparative Example 1 2 3 4 5 6 7 1 2 3 CoP* (A) P1 33P2 35 27 20 23 20 P3 20 33 20 P4 26 (B) P5 P6 50 69.5 59 50 69 57 57 5356 P7 68 (C) P8 10 10.5 14 17 11 19 13 14 13 12 P9 5 4 7 5 b/a 1.4 3.52.2 1.5 3.5 2.9 2.5 1.6 2.2 3.4 (a + b)/c 8.5 8.5 6.1 4.9 8.1 4.1 6.26.1 6.3 7.3 Ia** Color-rendering 75% 75% 77% 79% 76% 79% 78% 75% 67% 66%properties (ratio with respect to NTSC) Brightness/ 29.4 30.2 31.8 30.532.9 31.4 32.3 24.1 26.9 27.2 luminous flux Htc***  50° C. 99% 100%  99%99% 100%  99% 99% 98% 98% 99% 100° C. 97% 98% 97% 96% 97% 97% 97% 96%96% 97% 150° C. 92% 96% 95% 93% 96% 94% 94% 91% 91% 94% Lr**** 500 hrs98% 100%  100%  99% 100%  99% 99% 98% 98% 99% 2,000 hrs   95% 99% 98%96% 99% 97% 97% 94% 94% 95% Comparative Example 4 5 6 7 8 9 10 11 CoP*(A) P1 P2 19 34 26 20 P3 22 36 31 18 P4 (B) P5 68 P6 60 70 54 49 61 5272 P7 (C) P8 10 10 19 8 22 10 12 P9 18 3 b/a 2.7 3.7 1.5 1.4 2.0 2.0 4.03.4 (a + b)/c — 8.9 9.0 4.4 11.5 3.5 9.0 7.3 Ia** Color-rendering 67%65% 73% 70% 65% 66% 65% 74% properties (ratio with respect to NTSC)Brightness/ 24.8 28.0 27.3 26.7 26.3 27.0 28.1 23.7 luminous flux Htc*** 50° C. 99% 99% 97% 97% 99% 99% 98% 99% 100° C. 97% 97% 93% 94% 97% 97%97% 97% 150° C. 93% 94% 85% 86% 94% 94% 92% 94% Lr**** 500 hrs 99% 99%95% 96% 99% 98% 98% 99% 2,000 hrs   96% 97% 88% 89% 97% 94% 95% 97%“CoP*” means “Composition of the phosphor” “Ia**” means “Initialassessment” “Htc***” means “High-temperature characteristics” “Lr****”means “Long-term reliability”

The phosphor in Example 1 was a composition obtained by mixing phosphorP2 in Table 1 by 35 mass % as the silicate phosphor (A), phosphor P6 inTable 1 by 50 mass % as the oxynitride phosphor (B), and phosphor P8 inTable 1 by 10 mass % as the oxynitride phosphor (C), and by addingBR-102C by Mitsubishi Chemical Corporation by 5 mass %. In Table 2, thevalues of P1 to P9 in “Composition of the phosphor” represent masspercentage. To mix the phosphors, 2.5 g of the phosphors in total wasmeasured and mixed in a vinyl bag, and the mixture was then mixed with47.5 g of silicone resin (OE6656 by Dow Corning Toray) using a planetarycentrifugal mixer (“Awatori Rentaro” ARE-310 [registered trademark] byTHINKY). “b/a and (a+b)/c” in Table 2 are calculated values by assumingthat a represents the amount of the silicate phosphor (A), b representsthe amount of the oxynitride phosphor (B), and c represents the amountof the oxynitride phosphor (C).

To mount the phosphor to an LED, the LED was placed at the bottom of aconcaved package main unit, wire bonding with the electrode on asubstrate was performed, and then the mixed phosphors were injectedusing a micro-syringe. After the phosphor was mounted and hardened at120° C., post-curing was performed at 110° C. for 10 hours for sealing.As the LED, the one having an emission peak wavelength of 448 nm and achip in size of 1.0 mm×0.5 mm was used.

The assessment shown in Table 2 will hereinafter be described.

As the initial assessment in Table 2, color-rendering properties wereadopted as one of the initial assessment. To assess the color-renderingproperties, color reproduction range was used, and represented by thearea (%) with respect to NTSC standard on the color coordinate. Thelarger the value, the higher the color-rendering properties. The passingcriterion of the assessment is 72% or higher, which is the conditionadopted for general LED-TVs.

The value of the brightness in Table 2 was assessed by the luminous flux(lm) at 25° C. The measurement taken after the current of 60 mA wasapplied for 10 minutes was adopted. The passing criterion of theassessment is 25 lm or higher. Since this value fluctuates depending onthe measuring device used and conditions, the value was set bymultiplying the lower limit value of each Example by 85% in order tomake relative comparison with the Examples.

The high-temperature characteristics in Table 2 were assessed based onattenuation properties with respect to the luminous flux at 25° C.Luminous flux was measured at 50° C., 100° C., and 150° C., and themeasurements were represented as the values with respect to the valuemeasured at 25° C., which was regarded as 100%. The passing criterion ofthe assessment was 97% or higher at 50° C., 95% or higher at 100° C.,and 90% or higher at 150° C. These values are not global standardvalues, but considered to be a guideline for highly reliablelight-emitting devices.

The long-term reliability in Table 2 is expressed by the value ofattenuation of luminous flux. The phosphors were left as they were at85° C. and 85% RH for 500 hrs. and 2,000 hrs., respectively, they werethen taken out and dried at a room temperature, and their luminous fluxwas measured and expressed in the percentage with respect to the initialvalue, which is regarded as 100%.

The passing criteria of the assessment is 97% or higher for 500 hrs.,and 94% or higher for 2,000 hrs. These values cannot be achieved only bythe silicate phosphor.

As shown in Table 2, the Examples of the present invention exhibitedrelatively good color-rendering properties and luminous flux values, andexhibited relatively small attenuation of luminous flux even when storedin a high-temperature or high-temperature/high-humidity environment fora long time.

Comparative Example 1 of the present invention had a small luminous fluxvalue, and Comparative Examples 2, 3, and 4 had lower color-renderingproperties. In addition, Comparative Examples 5 and 8, where the amountof each phosphor fell outside the range of the present invention,exhibited extremely small color-rendering property values with respectto NTSC standard. Similarly, Comparative Example 6 was inferior inhigh-temperature characteristics and long-term reliability. Inparticular, Comparative Example 7, where the amount of oxynitridephosphor B added was too small, exhibited inferiority in all ofcolor-rendering properties, luminous flux, high-temperaturecharacteristics, and long-term reliability, which is why its use for thebacklight of a white LED is difficult. Furthermore, Comparative Example9, where the amount of oxynitride phosphor C added was too much,exhibited lower color-rendering property and luminous flux values.Comparative Example 10, where the ratio of the silicate phosphor A tothe oxynitride phosphor B fell outside the range, exhibited significantdecrease in luminous flux value in the test of high-temperaturecharacteristics and long-term reliability, causing the reliability ofthe LED package to become low. It can hardly be used for products suchas TVs and monitors.

INDUSTRIAL APPLICABILITY

The phosphor of the present invention is used for a white light-emittingdevice. The white light-emitting device of the present invention is usedfor the backlight of LC panels, illuminating devices, signaling systems,and image display devices.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A phosphor, comprising: a silicate phosphor (A) having a peakwavelength at least 525 nm but not higher than 535 nm and fluorescenceintensity at least 250% but not higher than 270%; an oxynitride phosphor(B) having a peak wavelength at least 540 nm but not higher than 545 nmand fluorescence intensity at least 260% but not higher than 280%; andan oxynitride phosphor (C) having a peak wavelength at least 645 nm butnot higher than 655 nm, wherein, the amount of the silicate phosphor (A)is at least 20% but not higher than 35% by mass; the amount of theoxynitride phosphor (B) is at least 50% but not higher than 70% by mass;and the amount of the oxynitride phosphor (C) is at least 10% but nothigher than 20% by mass.
 2. The phosphor as set forth in claim 1,wherein assuming the amounts of the silicate phosphor (A) and that ofthe oxynitride phosphor (B) are a and b, respectively, the ratiosatisfies 1.5≦b/a≦3.5.
 3. The phosphor as set forth in claim 1, whereinassuming the amounts of the silicate phosphor (A) and that of theoxynitride phosphors (B) and (C) of the phosphor are a, b, and c,respectively, the ratio satisfies 4.0≦(a+b)/c≦8.2.
 4. The phosphor asset forth in claim 1, wherein the oxynitride phosphor (B) is β-SiAlON,and the oxynitride phosphor (C) is CASN.
 5. The phosphor as set forth inclaim 3, wherein the oxynitride phosphor (B) is β-SiAlON, and theoxynitride phosphor (C) is CASN.
 6. The light-emitting device having thephosphor as set forth in claim 1 and an LED mounting the phosphor on itslight-emitting surface.